Torn Apart Engine Mounting

[Kafin Noe’man]

Has anyone experienced this?
Engine mounting area just torn apart in the middle of the flight












Good thing is, the wing and other parts are still intact.
I guess I need to make a new fuselage to have the maximum strength.


Best,
Kafin

[Clint Ormosen]

That nose looks like it’s been repaired before. The “break” lines on the doublers look like awfully clean lines.

[Doug Moisuk]

Where there maple or hard wood motor mounts? It looks like plywood.

[fred cesquim]

looks like the fiber board exerted a lot of stress on same places and due to heavy vibration stress cracked the nose. think aboiut the engine vibrating the nose and the sharp corners of the boards denting the plywood slowly....

[Dan McEntee]

That nose looks like it’s been repaired before. The “break” lines on the doublers look like awfully clean lines.

    Kafin, is this the banshee that you have been flying? i will agree with Clint, the way the break in the fuselage looks is awful peculiar. It might just be the result of too many breaks from crashes and not being repaired correctly. Just another lesson learned along the way. One thong to consider is , would this be a good candidate for a, R/C type or radial mount?  A firewall made from 1/4" plywood, (at least, maybe thicker,) is grafted and attached to the nose after the nose has been sanded straight and square. re-enforcing blocks or gussets can be installed on the inboard side of the fuselage, and dowels installed and epoxied through the plywood and into the fuselage where ever the wood in most dense. Find a plastic R/C mount like a Dave Brown of something else, make a plywood firewall that is nice and shapely to it, mount the engine mount to the firewall with screws and blind nuts, then secure the firewall to the fuselage as straight, square and solid as you possibly can, and you can get some more life out of the airplane. You can even mount the engine upright, inverted, or side winder like it was. It will just take s ome thought and planning.
   Type at you later,
    Dan McEntee

[Brett Buck]

I have to say that I have never seen anything like that on a SIG product with SIG-quality materials. I have seen something exactly like it on Ringmasters, with the poor quality double material and the maple just under the engine cutout.

    I strongly suggest fixing this. If it was me, I would splice on an entire new nose, taking care to use proper materials - 1/16 or 3/32 aircraft plywood doublers, and 1/2x3/8 sugar maple/rock maple mount material.

     Cut off the existing nose at the wing with 45-degree cuts top and bottom
    strip off any remaining doubler material and paint and glue back to about the trailing edge of the wing.
   Cut a new nose to fit your cuts from 1/2" balsa, tack in place, and mark the motor mount cutouts to make sure they will wind up parallel to the wing.
    Pop the nose back off, cut out the motor mount and slots for the maple bearers.
    Cut out doublers that go to about the trailing edge of the wing, with 45 degree angles on the tail end, and that fit around the wing closely.
    Remount the nose, glue in the motor mounts, and when it is all solid, apply the doublers. You will have to distort them to get around the high point of the wing. Use 30-minute epoxy for all gluing.
    Once you have it all together, file/sand the nose to the final shape.
    Drill the engine mount holes and the mount holes for the landing gear and tank.
    Fiberglass the entire nose with 3/4 ounce glass and epoxy, finish.
    Cut down your G10 doublers to be about 1/2" wide and about 1/2" longer than the motor mount lugs. Drill holes for the screws to go through, but do not glue them in place, just let them float under the engine, held by the screws.
    Reinstall LG and tank, good to go.

    Another note - keep a very close eye on that DuBro fuel filter. They are notorious for coming apart, the plastic part falling out of the barrel or leaking air. If it is loose, push it in as far as you can, crimp the end of the aluminum over the end of the plastic, and then dribble epoxy around the rear end of it for a seal.

    Brett

[John Carrodus]

Hi Kafin

Yes, about half a century or more ago, a young kid I know smashed up his stunt Showman. The repairs were not done correctly and the same thing happened to him a few flights later when the engine decided to swap codes and go freeflight!

Looking back on your photos , it appears the problem is clear in the picture showing you regluing the engine mount area and holding it all together with a couple of bulldog clips. Your patches on each side were far too short, and I not the balsa appears very soft short grained stuff.

Basically you had an engine running at about 9K, producing around one HP being held in place with soft balsa and a couple of maple toothpicks in between a couple of short packers.

The Banchee /P40 was doomed before takeoff- unfortunately. Thank heavens it didn't all come adrift in your face on the ground!
All good learning !

The guys above have clearly given you a good repair process to follow. Good luck.

[Tim Wescott]

This is just to add to what everyone has said so far about repairs.  It's about the "why", because the "what" and "how" have already been answered:

The nose construction on a profile is designed to take all that vicious vibration from the engine and distribute it over the rest of the airframe in a way that (A) is rigid, (B) won't break, and (C) is as light as possible.

So the maple motor mounts are there because sugar maple* is super-hard and super tough.  They take the pounding from the engine itself.  They're long enough (at least on a Sig kit) to transfer that vibrational force to the plywood doublers. 

The plywood doublers are there because if you just glued maple mounts to balsa, the transition in strength would be too sharp, and the mounts would vibrate out of the fuselage in short order.  They take the force from the maple mounts, and they spread it across the entire height of the fuselage -- and while they're at it, they give a bit of strength in a crash.

The rest of the fuselage is there for carrying flight loads -- that's why the doublers end about where the wing starts, so that the plane isn't too heavy to fly.

* It really needs to be sugar maple -- there's a lot of trees called "maple", and they have woods of very different properties.  There may be other woods that are suitable for this job, but the only one that I can guarantee you is right is -- sugar maple.

[Peter in Fairfax, VA]

The doublers need to be continuous from near the main wing spar to the front of the plane.

I had a similar failure recently and have repaired that plane by cutting new doublers.  To remove the old doublers, heat up a putty knife with a torch and plunge it.  The glue will melt, even if epoxy.  Do it outdoors.

Peter

[Peter in Fairfax, VA]

Dan's idea to convert to an R/C firewall style mount is a good one.  Might be much easier than ungluing doublers, which is what I did recently.

[Kafin Noe’man]

looks like the fiber board exerted a lot of stress on same places and due to heavy vibration stress cracked the nose. think aboiut the engine vibrating the nose and the sharp corners of the boards denting the plywood slowly....

Yes, this is what I thought as well.
I like the idea of having a very strong surface to prevent the doubler 'sinking & crushing' caused by tightening the engine bolts, and it actually did. But one thing I wasn't aware was it probably cracked the inside hardwood and balsa.

[Kafin Noe’man]

Kafin, is this the banshee that you have been flying? i will agree with Clint, the way the break in the fuselage looks is awful peculiar. It might just be the result of too many breaks from crashes and not being repaired correctly.

Yes, sir. It's the Banshee that I have been flying. It's true that this plane has gone through so many crashes and I believe I wasn't aware if those crashes might have caused some internal structural damage.

Find a plastic R/C mount like a Dave Brown of something else, make a plywood firewall that is nice and shapely to it, mount the engine mount to the firewall with screws and blind nuts, then secure the firewall to the fuselage as straight, square and solid as you possibly can, and you can get some more life out of the airplane. You can even mount the engine upright, inverted, or side winder like it was.

Is this approach like what we often see on the 1/2-A planes?

[Kafin Noe’man]

I have to say that I have never seen anything like that on a SIG product with SIG-quality materials.

Brett, thank you for your idea as well.
This plane has gone through so many crashes and repairs.
The fuselage and its engine mounting area were not built with SIG materials, I scratched built it after my first crash last year.

It actually flew okay up until I crashed again earlier this year and I did some repair and adding fiber board to have a very strong surface to prevent the doubler from 'sinking & crushing' caused by tightening the engine bolts, and it actually did. However, it seems the fiber board exerted a lot of stress to the inside hardwood & balsa.

[Kafin Noe’man]

Looking back on your photos , it appears the problem is clear in the picture showing you regluing the engine mount area and holding it all together with a couple of bulldog clips. Your patches on each side were far too short, and I not the balsa appears very soft short grained stuff.

Basically you had an engine running at about 9K, producing around one HP being held in place with soft balsa and a couple of maple toothpicks in between a couple of short packers.

Hi John, yes, I also suspect the balsa and the hardwood I used were not good enough. It wasn't the balsa and hardwood from the SIG anymore since I had to make a new fuselage after my first crash last year.

I will take my time to repair it since I have another planes to trim and fly 

[Kafin Noe’man]

This is just to add to what everyone has said so far about repairs.  It's about the "why", because the "what" and "how" have already been answered:

The nose construction on a profile is designed to take all that vicious vibration from the engine and distribute it over the rest of the airframe in a way that (A) is rigid, (B) won't break, and (C) is as light as possible.

So the maple motor mounts are there because sugar maple* is super-hard and super tough.  They take the pounding from the engine itself.  They're long enough (at least on a Sig kit) to transfer that vibrational force to the plywood doublers. 

The plywood doublers are there because if you just glued maple mounts to balsa, the transition in strength would be too sharp, and the mounts would vibrate out of the fuselage in short order.  They take the force from the maple mounts, and they spread it across the entire height of the fuselage -- and while they're at it, they give a bit of strength in a crash.

The rest of the fuselage is there for carrying flight loads -- that's why the doublers end about where the wing starts, so that the plane isn't too heavy to fly.

* It really needs to be sugar maple -- there's a lot of trees called "maple", and they have woods of very different properties.  There may be other woods that are suitable for this job, but the only one that I can guarantee you is right is -- sugar maple.

Tim, thank you for your explanation. I'll take more attention to make sure I have the proper material for the engine mounting part.

[Brett Buck]

Brett, thank you for your idea as well.
This plane has gone through so many crashes and repairs.
The fuselage and its engine mounting area were not built with SIG materials, I scratched built it after my first crash last year.

It actually flew okay up until I crashed again earlier this year and I did some repair and adding fiber board to have a very strong surface to prevent the doubler from 'sinking & crushing' caused by tightening the engine bolts, and it actually did. However, it seems the fiber board exerted a lot of stress to the inside hardwood & balsa.

Live and learn, right?  That's why stunt is mostly about attention to detail, there are a million little things like this that can either help or hurt you.


   Brett

     

[Ken Culbertson]

I just noticed on the picture what caused the vibration - it was the one bladed prop. 

Ken

Seriously, replace the entire nose.  If the plane flies well it will be worth it.  You are reaching the point where the mean time between crashes is going to keep growing.

Ken

[Dan McEntee]

Yes, sir. It's the Banshee that I have been flying. It's true that this plane has gone through so many crashes and I believe I wasn't aware if those crashes might have caused some internal structural damage.

Is this approach like what we often see on the 1/2-A planes?

    Yes, similar to what you see on the 1/2A models, but more solid. There have been designs with this type of nose , the one most are familiar with is Ted Fancher's Imitation. It had a 'flat nose" with a fire wall radial mount to allow easy changing of engines. It was published in our AMA's Model Aviation Magazine, and some one may have posted scans of it on here, so a good search of the forum may turn it up. The biggest thing I would caution you about going that route is to make sure what is left of the fuselage is still solid and not fuel soaked. Then make sure that you can mount the engine where it will be about in the same position and that the thrust line of the engine is still in line with the wing. If what you have left of the fuselage is too fuel soaked, or dos not look solid, i would just cut the wing and tail off of it and make a new fuselage is you have the balsa wood for it. It is really difficult to assess what the damage is and how to explain the process and go about it just from looking at photos, but take you time and look things over as closely as you can. A whole new fuselage might be the easiest way to go.
  Good luck with it,
   Dan McEntee

[Tim Wescott]

Tim, thank you for your explanation. I'll take more attention to make sure I have the proper material for the engine mounting part.

I don't know where you're located.  If you can't easily get sugar maple (which is a North American species) then start a thread on the Engineering or Building boards about how to figure out if a local wood is a good substitute.  I'm sure folks have looked into other things you can use.

[John Carrodus]

Hi Kafin
Any local /native hardwood will probably do for your purposes. Kwila? the weight is not going to mess up the performance for what you are doing at the moment. Long grain is good and drill bolt holes through the layers , not along them.
Good repairing.
John

[Tim Wescott]

... Any local /native hardwood ...

Nerdy terminology alert!  "hardwoods" vs. "softwoods" are probably the most misleading botanical term ever.  Because balsa is a "hardwood".  Unlike the famously-strong yew, which is a "softwood".

You want wood that is hard.  Which (forgive me) is probably going to be a hardwood.

You want something tight grained, dense (35-55 pounds per cubic inch), and long-grained like John said.  All the alternatives that come to my mind other than mahogany are North American or European species, so I'm zero help.

[John Park]

Nerdy terminology alert!  "hardwoods" vs. "softwoods" are probably the most misleading botanical term ever.  Because balsa is a "hardwood".  Unlike the famously-strong yew, which is a "softwood".

You want wood that is hard.  Which (forgive me) is probably going to be a hardwood.

You want something tight grained, dense (35-55 pounds per cubic inch), and long-grained like John said.  All the alternatives that come to my mind other than mahogany are North American or European species, so I'm zero help.

In Britain, beech is what has always been available commercially as engine-bearer material.  I'm lucky to have some offcuts of 150-year-old salvaged mahogany, which is as good as beech but a little lighter.

[Ken Culbertson]

I have used both Mahogany and Oak from a broken baseball bat when Maple was not available.  The point is vibration transfer and crush strength.  A "softer" hardwood with steel inserts in the holes will work if you can't find a really "hard" one.  Check with your furniture industry.  There are some pretty hard woods in your part of the world.  The good news in all of this extra weight is in the right place.  I can't remember if the banshee used long mounts or just the short ones in the cutout area.  It is important to the wing fuselage joint that the mounts be longer than the cutout hole and a tight fit so that the vibration is distributed.

Bet you already have it fixed but advise is free here!!

Ken

[M Spencer]

A NOSE DOUBLEr - back to the wing Main Spar - can absorb Vibration . Early Bird plan shows typical set up - note the packer in the front .
The combat jobs theyed wrap them with Gauze Bandage & Balsa Cement to toughen em up for the vertcal landings in the mud & otherwise .


the idea is to have a " engine Bed " which is why they use ' crutches ' these days in F2B ships .




FIBREGLASSING the NOSE is not unusual on STUNT SHIPS . Prop Strike & or out of balance PROP & it'll shake itself to death . Hence Engine Cables in Combat .

you sort of try to ' tie it all in ' - together - throw the strain back aft .

[Peter in Fairfax, VA]

Kafin,

I had a similar failure near the end of last season, as shown below.  And all is now repaired, and better for it.

In my case, the Brodak ARF "clamp bar" style mount design allowed for fuel to soak the bearers where they are penetrated for fasteners.  Broke upon starting.

But the failure was an opportunity to enhance the plane.  I cut plywood doublers that run from the spar to the nose, continuously.  A cheek cowl shaped from light balsa serves as a vibration deadener and adds an aesthetic quality, however small.

The building technique which was new to me was the use of a hot knife to disassemble the old doublers and bearers.  I'm fortunate that a local leader, Scott Richlen, runs an open shop in Winter.  Though I appreciate that the clarity of your posts draws in a global community.

Peter

[Peter in Fairfax, VA]

The repair in progress.

[Peter in Fairfax, VA]

Needed nose weight before repair, so new cheek block was just right.  The Pathfinder balanced 1/4" behind the spar and flew just fine right off the bench.